Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is an inkjet print head used in an ink jet printer. Ink jet printers continue to be improved as the technology for making their micro-fluid ejection heads continues to advance.
In the production of conventional thermal ink jet print cartridges for use in ink jet printers, one or more micro-fluid ejection heads are typically bonded to one or more chip pockets of an ejection device structure. A micro-fluid ejection head typically includes a fluid-receiving opening and fluid supply channels through which fluid travels to a plurality of bubble chambers. Each bubble chamber includes an actuator such as a resistor which, in the case of a resistor, when addressed with an energy pulse, momentarily vaporizes the fluid and forms a bubble which expels a fluid droplet. The micro-fluid ejection head is provided by an ejector chip and a nozzle plate having a plurality of discharge orifices formed therein attached to the chip. The chip and nozzle plate assembly are adhesively attached to an ejection device structure that provides fluid flow to the ejection head.
A container, which may be integral with, detachable from or remotely connected to (such as by tubing) the ejection device structure, serves as a reservoir for the fluid and includes a fluid supply opening that communicates with a fluid-receiving opening of a micro-fluid ejection head for supplying ink to the bubble chambers in the micro-fluid ejection head.
During assembly of the micro-fluid ejection head to the ejection device structure, an adhesive is used to bond the ejection head to the ejection device structure. The adhesive “fixes” the micro-fluid ejection head to the ejection device structure such that its location relative to the ejection device structure is substantially immovable and does not shift during processing or use of the ejection head. The bonding and fixing step is often referred to as a “die attach step”. Further, the adhesive may provide additional functions such as serving as a fluid gasket against leakage of fluid and as corrosion protection for conductive tracing. The latter function for the adhesive is referred to as part of the adhesive's encapsulating function, thereby further defining the adhesive as an “encapsulant” to protect electrical component connections, such as a flexible circuit (e.g., a TAB circuit) attached to the micro-fluid ejection head, from corrosion.
However, the micro-fluid ejection head and the ejection device structure typically have dissimilar coefficients of thermal expansion. For example, micro-fluid ejection heads may have silicon or ceramic substrates that are bonded to an ejection device structure that may be a polymeric material such as a modified phenylene oxide. Thus, the substrate adhesive (e.g., die bond), nozzle plate adhesive, and encapsulant must accommodate both dissimilar expansions and contractions of the micro-fluid ejection head and the ejection device structure, and be resistant to attack by the ejected fluid.
Conventional adhesive and encapsulant materials tend to be non-flexible and brittle after curing due to high temperatures required for curing and relatively high shear modulus of the adhesive materials upon curing. Such properties may cause the adhesive or encapsulant materials to chip or crack. It may also cause the components (e.g., micro-fluid ejection head and/or ejection device structure) to bow, chip, crack, or otherwise separate from one another, or to be less resilient to external forces (e.g., chips may be more prone to crack when dropped). For example, during a conventional thermal curing process, the ejection device structure typically expands before a conventional substrate adhesive and encapsulant material are fully cured. The adhesive and encapsulant materials thus move with the expanding device structure, wherein the adhesive and encapsulant materials cure with the device structure in an expanded state. Upon cooling the device structure, the device structure contracts and, with rigid, cured adhesives or rigid, cured encapsulant materials, high stress may be induced onto the ejection head structure to cause the aforementioned bowing, chipping, cracking, separating, etc.
Such adverse effects as bowing, chipping, cracking, separating, etc., may be even more pronounced as the substrates for the device structure are made thinner. Among other problems, such events may result in fluid leakage, corrosion of electrical component, and poor adhesion as well as malfunctioning of the micro-fluid ejection heads, such as misdirected nozzles. Moreover, attempts to make adhesive materials and encapsulant materials more flexible after curing often lead to materials that are less resistant to chemical degradation by the fluids being ejected.
Accordingly, a need exists for, amongst other things, micro-fluid ejection heads containing adhesive and encapsulant materials that are effective to reduce bowing or warping of ejection heads, and to improve the resistance of the ejection heads to corrosion of electrical components and impact damage due to dropping or other mishandling of the ejection heads.
With regard to the foregoing and other object and advantages, various embodiments of the disclosure provide a micro-fluid ejection head structure, methods of making micro-fluid ejection head structures having improved operability, and methods for improving the durability of micro-fluid ejection head structures. An exemplary micro-fluid ejection head structure includes a micro-fluid ejection head having a substrate and nozzle plate adhesively attached adjacent to a substrate support using a substrate adhesive, such as a die bond adhesive. The nozzle plate is adhesively attached adjacent to the substrate with a nozzle plate adhesive. An encapsulant material is adjacent to the ejection head and substrate support structure. The cure method for this material could utilize, for example, one or more of the following cure mechanisms: thermal cure, photosensitive cure, microwave cure, infrared (IR) cure, moisture cure, room temperature cure, actinic radiation cure (visible light, ultraviolet (UV) light, electron beam, x-ray, gamma-ray, beta-ray and the like), or multi- or dual-cure systems such as UV-initiated and thermal completed cure mechanisms. Each of the substrate adhesive and the encapsulant material, after curing, have a Young's modulus of less than about 2000 MPa, a shear modulus at 25° C. of less than about 15 MPa, and a glass transition temperature of less than about 90° C.
Additional embodiments provide a method for reducing bowing or warping of a micro-fluid ejection head component. According to one such method, a nozzle plate is adhesively bonded adjacent to a substrate with a nozzle plate adhesive to provide a nozzle plate/substrate assembly. The nozzle plate/substrate assembly is adhesively bonded in a pocket of a substrate support using a substrate adhesive. Electrical connections to the nozzle plate/substrate assembly are encapsulated with an encapsulant material adjacent to the nozzle plate/substrate assembly and substrate support. The nozzle plate adhesive, the substrate adhesive, and the encapsulant material are cured wherein at least the substrate adhesive and the encapsulant material are substantially flexible after curing.
Other exemplary embodiments may provide a method for improving micro-fluid ejection head durability. The exemplary method includes adhesively bonding a nozzle plate adjacent to a substrate with a nozzle plate adhesive to provide a nozzle plate/substrate assembly. The nozzle plate/substrate assembly is adhesively bonded in a pocket of a substrate support using a substrate adhesive. Electrical connections to the nozzle plate/substrate assembly are encapsulated with an encapsulant material that is adjacent to the nozzle plate/substrate assembly and substrate support. The nozzle plate adhesive, the substrate adhesive, and the encapsulant material are cured, wherein the nozzle plate adhesive, the substrate adhesive, and the encapsulant material are substantially flexible after curing. An advantage of the foregoing exemplary construction should be that the micro-fluid ejection head may withstand a greater drop height than an ejection head made in the absence of substantially flexible encapsulant material and substantially flexible adhesives (The drop height is the height from which a micro-fluid ejection head can function properly after a fall).
Advantages of the exemplary embodiments may include, but are not limited to, a reduction in ejector chip substrate bow, an increase in ejector head durability, increased planarity of the ejector head nozzle plate, printhead assembly planarity, and the like. The planarity of an ejector head nozzle plate is defined as the slope of each fluid ejection nozzle. Other advantages may include the provision of adhesives and encapsulant materials having improved mechanical, adhesive, and corrosion resistance properties. Reduced stresses, which may reduce ejection head fragility, may be present in the ejector head substrates due to the presence of improved encapsulant material and/or substrate adhesives according to the disclosed embodiments.